There is an increasing need nowadays for rotors or rotary members to be properly balanced, in particular when such a member is intended to be operated at a high speed of rotation. For the purposes of balancing a rotary member, as will be readily appreciated, it is first necessary to detect and measure the unbalance thereof. A typical form of apparatus for the measurement of unbalance on a rotary member comprises a rotary member mounting means which is capable of oscillating in a measurement direction and in which the rotary member is rotatably mounted for the measurement operation. The rotor can be driven in rotation by a belt drive in the measurement operation, and a measurement transducer device detects forces or oscillations produced by the rotary member during rotation thereof, which are operative in the measurement direction, and supplies a corresponding signal for unbalance measurement.
In a measurement station which includes a measuring apparatus of the above-indicated kind, and more especially in automatic balancing installations, the belt drive for driving the rotary member in rotation bears against the rotary member at the underside thereof in tangential relationship therewith, or has the belt of the belt drive passing around a small portion of the periphery of the rotary member, also at the underside thereof. The pulling direction of the belt or the belt drive, for driving the rotary member in rotation by virtue of the pulling force applied thereto, is the same as the measurement direction in which the measurement transducer device on the rotary member mounting assembly detects forces or oscillations produced upon rotation of the rotary member. The pulling direction of the belt where it engages the rotary member and the measurement direction are disposed horizontally. That arrangement is intended in particular to ensure that the rotary member can be fitted into and removed from the rotary member mounting means, without being impeded by the belt drive. That is a consideration of major significance in particular in relation to automatic balancing installations in which balancing operations are to be carried out at a high cycle rate.
It has been found with the above-indicated measuring apparatus that, during the measuring run, forces which can affect the measurement result may occur synchronously with the speed of rotation of the rotary member.